Photoaffinity labeling. We propose to prepare a series of diazophosphonates, diazophosphonate esters and diasophosphate esters, and another series of phosphazides and related compounds, to test as photoaffinity labels with enzymes of phosphate metabolism. This work continues that begun last year by Dr. Charles McKenna. Effective specific labeling in these enzymes is unknown but highly desirable. We are also planning to prepare the diazoacetate and ethyldiazomalonate derivatives of pyridoxal phosphate, utilizing the phenolic hydroxyl group as a handle. These materials should bind tightly to various enzymes of amino acid metabolism (e.g., transaminase), since the binding involves the formation of covalent bonds (aldimine formation) as well as electrostatic binding at the phosphate residue. It may even prove possible to reduce the postulated aldimine without destroying the diazo function, so as to anchor the group in place. The products (with or without reduction) will then be photolyzed to produce photoaffinity labeling. Our project to identify the products of photoaffinity labeling in general by mass-spectrometric techniques will be continued. Other. We are continuing to seek specific chemical inhibitors for alkaline phosphatase, for the phosphodiesterase discovered and purified in these laboratories, and for acetoacetate decarboxylase. We are trying to prepare an affinity labeling column for the purification of orotidine-5-phosphate decarboxylase, in anticipation of mechanistic studies. The undersigned agrees to accept responsibility for the scientific and technical conduct of the project and for provision of required progress reports if a grant is awarded as a result of this application.